HYDRAULIC CIRCUITS (LATER)

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REMOTE NORMAL SHUTOFF

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TM-5-2815-232-14 Engine Diesel Caterpillar Model 3508 Manual

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SCHEMATIC NO. 13 (START-UP OVERRIDE)

HYDRAMECHANICAL PROTECTIVE SYSTEM

SYSTEMS OPERATION

HYDRAULIC CIRCUITS (LATER)

(With Check Valves in Diverter Valve)

Later hydramechanical protective systems

have hydraulic circuits that use check valves to

hold hydraulic pressure on (lock) the fuel shutoff

actuator in the "SHUTOFF" position, after the

engine has been shutdown. In this system, the

start-up override valve must be operated to

release the hydraulic pressure from the fuel

shutoff actuator before the engine can be

started. Also, make sure the air inlet shutoff is in

the open position before the engine is started.

The operation of these hydraulic circuits is -

the same as that of the earlier hydraulic circuits

except for the check valves in the diverter valve

for the fuel shutoff circuit.

START-UP OVERRIDE

Make Reference to Schematic No. 13

When operated, the start-up override valve

connects the fuel shutoff actuator circuit to drain.

This removes any hydraulic pressure on the

actuator so the governor can move the fuel

control linkage and the engine can be started.

Also, on hot restart, after severe operating

conditions, the engine oil pressure can increase

slowly. If the rate of pressure increase is too

slow, the protective system activates actuator (8)

to move the fuel control linkage to the

"SHUTOFF" position be- cause of a low engine

oil pressure fault. Therefore, an override of the

low engine oil pressure circuit is needed in the

protective system.

An electric solenoid or air operated start-up over-

ride valve (3) is installed in the diverter valve

return line. The valve is normally closed. When

start-up override valve (3) is operated, the outlet

of the di- verter valve is connected to drain. This

maintains a pressure drop across orifice (4) and

does not let the diverter valve shift to the

shutdown position. The fuel shutoff actuator line

is also connected to drain to make sure fuel

shutoff actuator (8) does not hold the governor

shutoff strap in the off position.

When start-up override valve (3) is not in use,

the engine oil circuit is put back into normal

operation as in Schematics No. 2 and No. 4.

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